The story of modern electronics is often equated with the
relentless advancement of the silicon-based microchips that process information
in our computers, phones and, increasingly, everything else. Moore’s law has
become a well-known summary of how those chips become ever more compact and
powerful.
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But electronics also have a critical, less-celebrated role in
modern life: directing the electricity that powers all of our gadgets. This field,
aptly called “power electronics,” is changing quickly as engineers switch to
power-control devices based not on silicon chips but on new materials that
handle electricity more quickly and efficiently. Some novel, post-silicon
devices are in use already, and better power electronics will become far more
important in the future as much of our economy switches from fossil fuels to
electricity. At a time when supply chains for silicon are severely kinked,
these newer materials have boomed.
This wave of new materials burst from the lab in 2017, when
Tesla faced a pivotal moment in its history. The company had released two
successful luxury car models, but in its effort to become a major automaker, it
gambled the company’s future on making a cheaper, mass-market vehicle.
When Tesla released its Model 3, it had a secret technical edge
over the competition: a material called silicon carbide. One of the key parts
of an electric car is the traction inverters, which take electricity from the
batteries, convert it into a different form and feed it to the motors that turn
the wheels. To get the pin-you-to-your-seat acceleration that Teslas are known
for, traction inverters must pump out hundreds of kilowatts, enough power to
supply a small neighborhood, while being dependable enough to handle
life-or-death highway use.
Although previous traction inverters had been based on silicon,
the Model 3's were made from silicon carbide, or SiC, a compound that contains
both silicon and carbon. STMicroelectronics, a European company that produced
the silicon carbide chips that Tesla used, claimed they could increase a
vehicle’s mileage range up to 10% while saving significant space and weight,
valuable benefits in automotive design. “The Model 3 has an air-resistance
factor as low as a sports car’s,” Masayoshi Yamamoto, a Nagoya University
engineer who does tear-downs of electric-vehicle components, told Nikkei Asia.
“Scaling down inverters enabled its streamlined design.”
The Model 3 was a hit, thanks in part to its groundbreaking power
electronics, and demonstrated that electric cars could work on a large scale.
(It also made Tesla one of the most valuable companies in the world.)
“Tesla made this fantastic move,” said Claire Troadec, an
analyst at Yole Développement, a high-tech research and consulting firm in
France, referring to the company’s switch to silicon carbide. “What they did in
a year and a half was really amazing.”
With Tesla’s fast rise, other automakers have moved aggressively
to electrify their fleets, pushed on, in many places, by government mandates.
Many of them are also planning to use silicon carbide not only in traction
inverters but in other electrical components such as DC/DC converters, which
power components such as air conditioning, and on-board chargers that replenish
the batteries when a car is plugged in at home. Silicon carbide costs much more
than silicon, but many manufacturers are concluding that the benefits more than
make up for the higher price.
In the niche of power electronics, which has sales of about $20
billion per year, silicon carbide is making significant inroads. Yole
Développement projects that the automotive market for silicon carbide will
increase to $5 billion in 2027 from its current total of a little more than $1
billion.
“We wouldn’t have had such a boom of electric vehicles without
silicon carbide,” said STMicroeletronics executive Edoardo Merli.
Better building blocks
Silicon and silicon carbide are useful in electronics because
they are semiconductors: They can switch between being electrical conductors,
as metals are, and insulators, as most plastics are. This ability makes
semiconductors the key materials in transistors — the fundamental building
blocks of modern electronics.
Silicon carbide differs from silicon in that it has a wide
bandgap, meaning that it requires more energy to switch between the two states.
Wide bandgap, or WBG, semiconductors are advantageous in power electronics
because they can move more power more efficiently.
Silicon carbide is the senior citizen of WBGs, having been under
development as a transistor material for decades. In that time, engineers have
started using younger upstart WBG materials, such as gallium nitride, or GaN.
In the 1980s, researchers used gallium nitride to create the world’s first
bright blue LEDs. Blue light comprises high-energy photons; gallium nitride,
with its wide bandgap, was the first semiconductor that could practically
produce photons with the sufficient energy. In 2014, three scientists were
awarded the Nobel Prize in physics for that innovation, which became ubiquitous
in devices such as TV screens and lightbulbs.
Lately, researchers have started using gallium nitride to
improve power electronics. The material reached commercial fruition over the
past few years in adapters for charging phones and computers. These adapters
are smaller, lighter, faster-charging and more efficient than traditional ones
that use silicon transistors.
“A typical charger that you buy for your computer is 90%
efficient,” said Jim Witham, CEO of GaN Systems, a Canadian company that
supplied the transistors in Apple’s gallium-nitride laptop chargers, which were
released last fall. “Gallium nitride is 98% efficient. You can cut power losses
by four times.”
Engineers are working on using WBG materials to better take
advantage of renewable energy sources. Solar cells and wind turbines rely on
inverters to feed electricity into a home or into the grid, and many companies
expect gallium nitride to do that job better than silicon. Enphase, a supplier
of inverters for solar-powered installments, is currently testing
gallium-nitride-based inverters to make sure they can hold up to harsh rooftop
weather conditions for decades. In one test, Enphase submerges inverters
underwater inside a pressure cooker, puts the pressure cooker inside a sealed
chamber and oscillates the temperature between 185 degrees and minus 40 degrees
Fahrenheit over the course of 21 days. If gallium-nitride devices survive the
challenges, Enphase co-founder Raghu Belur plans to make a fast shift to the
new material. “It’s absolutely headed in that direction,” he said.
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